1. Field of the Invention
The present invention relates to a pigment-containing ink that is suitable as a yellow ink for ink jet recording, and relates to an ink cartridge including the ink, and an ink jet recording method.
2. Description of the Related Art
Recently, there is a demand for further increasing light resistance of images obtained by ink jet recording method. As inks that can improve light resistance, pigment inks containing pigments have been used. However, the pigment inks are usually low in color developability of images compared to dye inks that contain dyes, and it is therefore necessary to develop a pigment ink that can achieve both high light resistance and good color developability. In particular, in yellow inks, it is difficult to form an image having both high light resistance and good color developability, that is, these properties are contradictory to each other.
For example, an ink containing both C.I. Pigment Yellow 74 and C.I. Pigment Yellow 128 is proposed for achieving both good color developability and high light resistance of images (see Japanese Patent No. 03455764). In addition, a recording method in which a high-density region is recorded with an ink containing C.I. Pigment Yellow 74 and a low-density region is recorded with an ink containing C.I. Pigment Yellow 128 is proposed for achieving both good color developability and high light resistance of images (see Japanese Patent Laid-Open No. 2000-345080).
Furthermore, pigment inks contain pigments in particle states and thereby have problems that the glossiness of images obtained is low compared to that of images formed with dye inks dissolving coloring materials in molecular states in aqueous media. A pigment ink containing a urethane polymer in addition to an acrylic polymer for dispersing a pigment is proposed for improving glossiness of images formed with the ink (see Japanese Patent Laid-Open No. 2006-070123).
As described above, yellow inks containing pigments as the coloring materials may be required to provide images having both good color developability and high light resistance and also having improved glossiness.
However, in the above-mentioned inks described in Japanese Patent No. 03455764 and Japanese Patent Laid-Open No. 2000-345080, though both the color developability and the light resistance of obtained images are improved, the glossiness of the images is still insufficient. Accordingly, the present inventors investigated application of the technology of further adding a urethane polymer described in Japanese Patent Laid-Open No. 2006-070123 to an ink containing C.I. Pigment Yellow 74 and C.I. Pigment Yellow 128 as described in Japanese Patent No. 03455764. However, it was confirmed that the glossiness of obtained images could not satisfy the level recently required.